Download Intrusive vs. Extrusive

Igneous Environments lecture 2a
Intrusive vs. Extrusive
• Melt that exists below the surface is
called _______ and rocks formed by
this process are ______ (pushed) into
preexisting rocks and referred to as
_________ _______
• Melt that is erupted on the surface is
called _____ and rocks formed by this
process are ________ (pushed) onto
the surface and referred to as
__________ ______
ERSC 3P21 Brock University Greg Finn 2005
Intrusive Environments
• Rising magma moves through
preexisting rock and crystallizes at
depth - Intrusive igneous rocks
• Rocks formed in this type of setting are
termed __________
– from Greek Plouton - god of the
underworld
• Results are observed at the surface due
to ___________
ERSC 3P21 Brock University Greg Finn 2005
Intrusive Environments
• Preexisting rocks are referred to as _______
rock or _______ rock
• The contact between the two is an ________
contact
• Chunks of country rock can be incorporated
into the magma forming _____________
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Intrusive Environments
• The hot magma comes in contact with
colder country rock
• country rock is _______ and may be ______
along the contact
• magma cools quickly along contact and
________ remainder of intrusion to allow for
________ cooling
COLD
HOT
From: Marshak 2001
ERSC 3P21 Brock University Greg Finn 2005
ERSC 3P21 Brock University Greg Finn 2005
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Intrusive Environments
From: Marshak 2001
Rising magma ( _________ - upward
excavation) into country rock creates the
magma chamber
Country rock is ______ and ________ by
the magma, with unmelted blocks forming
xenoliths within the magma
ERSC 3P21 Brock University Greg Finn 2005
Types of Intrusives
• Distinguished by shapes
• Tabular intrusions
– generally ________ features with _______
sides, extending over ______ to ____’s of
km, of uniform thickness ranging from mm
to 100’s of metres
• _________ intrusions are termed dykes
• _________ intrusions are termed sills
ERSC 3P21 Brock University Greg Finn 2005
DYKE
From: Marshak 2001
SILL
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
From: Marshak 2001
ERSC 3P21 Brock University Greg Finn 2005
ERSC 3P21 Brock University
GregHoffmann
Finn 2005
Paul
Types of Intrusives
• Where a sill is domed upwards a blisterlike intrusion results - a ___________
• _______ are ______ shaped intrusions
ranging in size from from 10’s of m to
10’s of km across
• Intrusion of numerous plutons in one
area creates a composite body - a
____________
– 100’s of km long X 10’s to 100’s of km wide
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Sierra
Nevada
Batholith
ERSC 3P21 Brock University Greg Finn 2005
Mount Whitney Crest, SN Batholith
ERSC 3P21 Brock University Greg Finn 2005
Types of Intrusives
• Intrusive igneous rocks form _________
the Earth’s surface
• We can observe them at present as
they are brought to the surface over
long periods of geologic time through:
•
•
•
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Intrusive Environments
Ash
Lava Flow
Sill
Dyke
Magma
Chamber
Laccolith
From: Marshak 2001
At an active volcano a magma chamber is present in the subsurface
and serves as the source of magma that forms dykes, sills, laccoliths
below ground, and lava and ash above ground.
ERSC 3P21 Brock University Greg Finn 2005
Intrusive Environments
From: Marshak 2001
As a result of crystallization, the magma chamber becomes a pluton.
The softer portions of the volcano erode, leaving wall-like dykes and
resistant lava plateaus.
ERSC 3P21 Brock University Greg Finn 2005
Intrusive Environments
From: Marshak 2001
As weathering and erosion continue the volcanic rocks and shallow
intrusions are removed and plutonic rocks are exposed.
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
From: Marshak 2001
ERSC 3P21 Brock University Greg Finn 2005
Intrusive vs. Extrusive
• Melt that exists below the surface is
called magma and rocks formed by this
process are intruded (pushed) into
preexisting rocks and referred to as
Intrusive Rocks
• Melt that is erupted on the surface is
called lava and rocks formed by this
process are extruded (pushed) onto the
surface and referred to as Extrusive
Rocks
ERSC 3P21 Brock University Greg Finn 2005
Extrusive Environments
• Not all volcanic eruptions are the same
so not all extrusive rocks are the same
• Volcanoes may erupt:
– __________________________________
__________________________________
__________________________________;
– __________________________________
_______________________________;
– _______________________________.
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Volcanic Eruptions
• Volcanic eruptions transfer material form the
Earth’s interior to its surface
• Material erupted falls into three categories:
– ______________
• sheets or mounds that flow onto the surface or sea floor
and then solidify
– _______________
• fragmented material thrown out of a volcanic vent and
lands on the ground surface or sea floor as a solid
– _______________
• elements or compounds that bubble out of the lava
ERSC 3P21 Brock University Greg Finn 2005
Extrusive Environments
ERSC 3P21 Brock University Greg Finn 2005
Lava and Lava Flows
• Lava displays a variety of compositions,
and are described using the range of
SiO2 content
– ________ lavas
• high SiO2, rhyolite
– ____________ lavas
• andesite
– __________ lavas
• low SiO2, basalt
• All are __________, SiO2-rich are
glassier than SiO2-poor,
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Lava and Lava Flows
• Viscosity (__________________) is
dependent on _____________ and
_____________:
• _______ the SiO2, the _____ the viscosity so
the ________ the ease with which it will flow
• ______ a lava, the _______ the viscosity
• More gas-rich a magma the _____ the viscosity
• Volcanic rock formed by extrusion is a
Lava Flow, and the ________ of the
resulting flow reflects the ______ of the
lava
ERSC 3P21 Brock University Greg Finn 2005
Increasing Viscosity
Lava and Lava Flows
Basaltic Flow
Andesitic Flow
Rhyolitic Dome
From: Marshak 2001
Rhyolitic Spire
ERSC 3P21 Brock University Greg Finn 2005
Basaltic Lava Flows
• Due to ___ viscosity, capable of flowing
great distances 10s to 100s of km
From: Marshak 2001
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Basaltic Lava Flows
• Surface textures of flow reflects the
timing of __________ relative to
____________
From: Marshak 2001
From: Marshak 2001
Pahoehoe (ropey)
Aa (blocky)
ERSC 3P21 Brock University Greg Finn 2005
Basaltic Lava Flows
• After the surface of
the flow cools, the
interior remains
molten and continues
to move downslope,
draining out and
leaving a ______
_______
From: Marshak 2001
ERSC 3P21 Brock University Greg Finn 2005
Basaltic Lava Flows
From: Marshak 2001
During the final
stages of cooling
the interior of the
lava flow contracts
and fractures into
roughly hexagonal
columns resulting
in __________
__________
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Basaltic Lava Flows
From: Marshak 2001
Copyright Peter Kresan
Basaltic lava
extruded under
water cools much
quicker than on
land and has a
distinctive _______
shape
Copyright Greg Finn
ERSC 3P21 Brock University Greg Finn 2005
Andesitic Lava Flows
• Due to ______ SiO2 content and _____
viscosity andesitic lava does not ___ as
easily as basaltic lava
• Andesitic lava moves 1-5 m/day and
rarely reaches lengths of 10 km
• Due to slow movement the outer
surface _________ while the interior
continues to _____ causing the surface
to break into angular blocks
ERSC 3P21 Brock University Greg Finn 2005
Andesitic Lava Flows
• Andesitic volcanic cones have _______
slopes than basaltic cones
From: Marshak 2001
Andesitic Flow
Copyright Greg Finn
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Rhyolitic Lava Flows
• Rhyolite lava is the most ______ due to
its _____ SiO2 content and _____
overall temperature
• Does not flow easily, tends to form a
_____ or _____ over the vent
Rhyolitic Dome
From: Marshak 2001
Rhyolitic Spire
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
Lava
dome in
crater
1984
ERSC 3P21 Brock University Greg Finn 2005
Pyroclastic Debris
• Fragmental material _______ at a
volcanic vent
• Come in a variety of sizes
• On a global scale has the largest
impact on the planet
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Pyroclastic Debris
Wind Direction
Stratospheric Haze
Rising Column
Falling
Lapilli
Collapsing
Column
Nuée Ardente
• Coarse material
falls _______ the
vent
• Finer material falls
________ from the
vent
ERSC 3P21 Brock University Greg Finn 2005
Pyroclastic Debris
• ______
• powder size
• _______________
• marble to plum
sized
• __________
• basketball to fridge
sized
• ________
• streamlined blocks
ERSC 3P21 Brock University Greg Finn 2005
Pyroclastic Debris
• During eruptions lava fountains into the
air and freezes into glassy rock before
falling to the ground
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Pyroclastic Debris
• Basaltic droplets form glassy beads
termed Pelé’s tears after the Hawaiian
goddess of ____________
• An accumulation of blocks is termed a
volcanic _____________
• Andesitic and rhyolitic eruptions eject
________ - sponge like volcanic glass
filled with air bubbles
ERSC 3P21 Brock University Greg Finn 2005
Pyroclastic Debris
Pelé’s Tears
Lapilli
From: Stromboli on-line
Copyright J. Alean
Copyright J.Aabech
Pumice
Volcanic Agglomerate
ERSC 3P21 Brock University Greg Finn 2005
Pyroclastic Debris
• Unconsolidated pyroclastic material is
termed _______
• Cemented pyroclastic material is termed
________
• Ash that falls gently from the air is
termed an ________________
• Where ash mixes with air it forms a fast
moving _______________ (nuée
ardente)
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Mount St. Helens
Pyroclastic
flow moving
from crater at
right to valley
floor travelling
at 60 mph and
at 800°C
ERSC 3P21 Brock University Greg Finn 2005
Volcanic Gas
• Most magmas contain dissolved gases
– H2O, CO2, SO2, H2S, etc.
• Gases come out of ________ as the
magma _______ to the surface and the
pressure _________
• Gas bubbles which become frozen in a
lava are termed _________
• Vesicles which are eventually filled as a
result of secondary processes are
termed _____________
ERSC 3P21 Brock University Greg Finn 2005
Igneous Textures
• ___________ - trapped air bubbles
• ___________ - filled vesicles
Vesicles
Amygdules
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Volcanic Gas
• In low viscosity lavas (basalt), trapped
bubbles can generally escape from the
liquid before ______________
• In ______ viscosity lavas (andesite and
rhyolite) the gas bubbles cannot escape
from the lava
• As the pressure ____, the gas _______
and may cause the violent eruption of
the volcano
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
Pre 1980
view - Peak
is at 2,950 m
elevation
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
May 18, 1980
Eruption
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Mount St. Helens
September
1980 peak
height now
2,550 m and
crater is 1.5
km across
following
May 18 1980
eruption
ERSC 3P21 Brock University Greg Finn 2005
Pre 1980
May 17, 1980
May 18, 1980
From Marshak 2001
ERSC 3P21 Brock University Greg Finn 2005
Immediate Area Effected
From: National Geographic, January 1981
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
From: Earth; 15 years later: Mount St. Helen’s
Immediate Area Effected
ERSC 3P21 Brock University Greg Finn 2005
Extent of Ash cloud/fall
From: National Geographic, January 1981
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
1982
eruption note ash
cloud, and
ash fall on
surface of
snow
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Mount St. Helens
Pyroclastic flow moving
from crater at right to
valley floor.
Travelling at 100 km/hr
and at a temperature of
800°C.
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
Pumice blocks
deposited at the
edge of a
pyroclastic flow
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
Lava dome
in crater
1981
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Mount St. Helens
Lava dome in
crater 1985,
Photo taken
from same spot
as previous
photo
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
Lava dome
1983. Note
geologist at
centre right
of photo.
Ground is
actually ash
covered
snow.
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
Mount St
Helens
from
Johnston
Ridge May
17, 1980
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Mount St. Helens
Mount St.
Helens from
Johnston
Ridge
September
1980
ERSC 3P21 Brock University Greg Finn 2005
Mount St. Helens
Mount St.
Helens from
Johnston
Ridge
September
1984
ERSC 3P21 Brock University Greg Finn 2005
Important Volcanic eruptions
•
•
•
•
•
•
•
•
Santorini ~1645 BC
Vesuvius 79 AD
Tambora 1515
Krakatoa 1883
Surtsey 1973
Mount St. Helens 1980
Pinatubo 1991
Olympus Mons (Mars)
ERSC 3P21 Brock University Greg Finn 2005
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Igneous Environments lecture 2a
Ejecta Volumes
From: National Geographic, January 1981
ERSC 3P21 Brock University Greg Finn 2005
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